It can be difficult to understand the significance of a cave-dwelling spider that no one ever sees, and why it would be more important than a highway interchange.

But for those who study species in the limestone caves below Bexar County, it's not hard at all.

The karst caves range in age from thousands of years to more than 100 million years. They are an incredibly difficult place for anything to live, with no light and few food sources.

The underground denizens have been separated from the world above ground for so long that they have evolved into unique species found nowhere else.

For science, these critters provide an irreplaceable study of how this part of the globe has changed. They are bellwethers for the health of the ecosystems that protect the groundwater the region depends on and are a testament to the tenacity of life.

For the Texas Department of Transportation, the species provide a constant challenge. To build roads, it has to cut through, fill in and cover the cave features the species depend on.

It is not known what can be learned from the Braken Bat Cave meshweaver.

That is why TxDOT now is studying what remains of the cave where the dime-size spider was found last month when construction crews unearthed a cave while digging an underpass for Texas 151 to go beneath Loop 1604.

If it can't find another cave with the same characteristics that is home to the same species, the $15.1 million highway project will have to be changed.

Dealing with federally protected endangered species is nothing new for TxDOT, said Gary Mowad, Texas state administrator for the U.S. Fish and Wildlife Service, which enforces the Endangered Species Act.

“They do a great job of trying to avoid impact,” he said of TxDOT.

If TxDOT can't avoid harming a species with one of its projects, it permanently protects similar habitat that is home to the same species to compensate, he said.

But the discovery of the Braken Bat Cave meshweaver, Cicurina venii, is slightly different.

The spider was believed to be extinct. The only cave it had ever been found in, Braken Bat Cave, a few miles from the construction site — and not to be confused with huge Bracken Bat Cave on the other side of the county — was filled in and paved over to make room for a housing development more than two decades ago.

In the 30 years since the species was first identified, no other cave had been found that it called home.

Now, by accident, TxDOT found the second.

If uncovering the cave has not significantly affected the feeding, breeding or sheltering behavior of the spider, TxDOT will have to change its plans so the cave will be left unharmed, Mowad said.

But if the cave is damaged or TxDOT can't change its plans, it will need to find another cave with the same species of meshweaver to protect.

More Information

“There is more legwork involved,” Mowad said. “They have to find a karst feature with the right species.”

That won't be easy, and last week TxDOT met with Fish and Wildlife in Austin. TxDOT would not share what happened at the meeting and sent out an email statement.

“It's so preliminary it's nearly impossible to narrow the options,” spokesman Josh Donat wrote. “We remain committed to developing a modified plan that accomplishes our goals of safety and addressing congestion while being a good steward of our natural resources,”

Fish and Wildlife is investigating to see if the Braken Bat Cave meshweaver was harmed by the construction and if any legal action needs to be taken against the state, said David Hubbard, resident Fish and Wildlife agent in charge for law enforcement in San Antonio.

He recently published papers that proved the closest relative to a blind, cave-dwelling fish in Madagascar actually was another limestone cave-dwelling fish 4,000 miles away, across the Indian Ocean in Australia.

The two fish species were separated by continental drift more than 100 million years ago.

Another blind cave-dwelling fish swims 2,000 feet below the streets of San Antonio. Satan eurystomus, a catfish named after the devil, is hypothesized to have escaped the cold of the last ice age by swimming into the springs, or has been left over from the shallow sea that once covered what now is Texas.

The Braken Cave meshweaver has a different story. It's closely related to eight other spider species in Bexar County, and others that live across Central Texas.

Like the finch species in the Galápagos Islands that have a different beak on each island to access different food sources, which helped Charles Darwin form his theory of evolution, the females of these Bexar County spiders all have different internal organs.

Why the organs are different is not known.

“Who knows what this spider can tell us?” Chakrabarty said. “In the end, we can build around this. But if we lose it, it's gone forever. We could learn a lot.”